The bacteria called Helicobacter Pylori (HP) are generally known as a cause of gastric ulcers and gastritis.
If the HP is present in the stomach of a patient, an antibiotic or the like should be administered to the patient for bacteria removal treatment. Therefore, it is important to check if the patient has the HP. The HP has a strong urease activity for decomposing urea into carbon dioxide and ammonia.
Carbon has isotopes having mass numbers of 12, 13 and 14, among which 13C having a mass number of 13 is easy to handle because of its non-radioactivity and stability.
If the concentration of 13CO2 as a final metabolic product in breath of the patient, more specifically, a 13CO2/12CO2 concentration ratio, can successfully be determined after 13C-labeled urea is administered to the patient, the presence of HP can be confirmed.
However, the concentration ratio of 13CO2 to 12CO2 in naturally occurring carbon dioxide is 1:100, making it difficult to accurately determine the concentration ratio in the breath of the patient.
There have been known methods for determining the concentration ratio of 13CO2 to 12CO2 or the concentration of 13CO2 by way of infrared spectrophotometry (see Japanese Unexamined Patent Publication No. 53-42890 (1978)).
In the method disclosed in Japanese Unexamined Patent Publication No. 53-42890, two cells respectively having a long path and a short path are prepared. The path lengths of the cells are adjusted such that a 13CO2 absorbance in one of the cells is equalized to a 12CO2 absorbance in the other cell. Light beams having wavelengths suitable for the respective analyses are applied to the respective cells, and the intensities of transmitted light beams are measured. According to this method, an absorbance ratio for the concentration ratio in naturally occurring carbon dioxide can be set at 1. Therefore, the absorbance ratio is changed correspondingly to a change in the concentration ratio. This allows detection of the change in the concentration ratio.    Patent Document 1: Japanese Unexamined Patent Publication No. 53-42890 (1978)    Patent Document 2: Japanese Unexamined Patent Publication No. 2002-98629    Patent Document 3: International Publication No. WO1997/14029 Pamphlet    Patent Document 4: International Publication No. WO1998/30888 Pamphlet    Patent Document 5: International Publication No. WO2002/25250 Pamphlet    Patent Document 6: International Publication No. WO2005/41769 Pamphlet